1. Field of the Art
The field of art to which this invention pertains is polymer production and compositions. More particularly, this invention relates to a two-step process, preferably performed in an aqueous suspension, to produce a polymer having high impact resistance and also prefereably having a high degree of transparency. This invention also relates to a composition of graft and random polymer mixtures.
2. Description of the Prior Art
Relevant prior art can be found in the following U.S. and British patents.
U.S. Pat. No. 3,426,103 (Class 260-880) relates to a method of making transparent polymers by dissolving a rubbery elastomeric polymer in monomers such as tertiaryalkylstyrenes and alkylstyrenes and acrylonitrile and heating the solution to inter-polymerize the monomers and the rubbery elastomeric polymer. At Column 2, lines 40 through 45 of that patent, there is discussion relating to the polymerization of the monomers which is carried out, in one alternate embodiment, by dispersing the monomers and the elastomeric polymer as droplets in an inert aqueous medium, i.e., in suspension, with a reaction temperature between about 60.degree. and 180.degree. C. The aqueous suspension process utilized in this patent, however, is distinguished from the present invention by an important factor - namely, applications in the present case utilize a two-step process in which a pre-polymerization step occurs followed by an additional addition of monomers. Preferably, both steps of applicants' process take place in an aqueous suspension. The addition of the monomers in applicants' second step is not disclosed in the subject patent.
U.S. Pat. No. 3,579,612 (Class 260-880) discloses a process in which the bulk polymerization of styrene and a rubbery polymer occurs, followed by suspending the resultant prepolymer in an aqueous medium containing a protective colloid and an extender.
British Pat. No. 1,046,646 (International Classification CO8f25/00) describes a novel two step process for preparing inter-polymers which comprises dissolving a rubbery component in a mixture of styrene and methyl methacrylate, prepolymerizing the resultant mixture to obtain a certain degree of conversion, and thereafter suspending the intermediate pre-polymer in an aqueous medium containing a minor quantity of a suspension stabilizer for complete polymerization to form inter-polymer beads which are subsequently recovered from the system.
British Pat. No. 1,105,187 (International Classification CO8f25/00) relates to a method of manufacturing butadienemethyl methacrylate-vinyl aromatic polymer compositions. In particular, methyl methacrylate is added and polymerized with the butadiene polymer. An aromatic vinyl compound is then added for additional polymerization; the entire process being carried out in an aqueous dispersion in which the diameter of substantially all of the particles in the dispersion of the butadiene polymer remains less than one-tenth of a micron which contributes to the excellent transparency of the resulting molded product.
None of the above four patents in any manner disclose or render obvious the process claimed by applicants. Specifically, applicants' process utilizes a two-step polymerization process which is preferably carried out in an aqueous suspension. It is noteworthy that applicants' process, in the second step thereof, adds additional monomer to the suspended pre-polymer. The cited art does not teach or disclose this.